Technical Abstract:
A serologically distinct avian metapneumovirus (aMPV) was isolated in the U.S. following an outbreak of turkey rhinotracheitis (TRT) during February of 1997. The newly recognized U.S. virus was subsequently demonstrated to be genetically distinct from European subtypes and was designated aMPV/C. We have determined gene nucleotide and predicted amino acid sequence of the cell attachment (G) glycoprotein of aMPV type C (aMPV/C; Colorado and three Minnesota isolates) by sequencing cloned cDNAs synthesized from intracellular RNA of aMPV/C infected cells. The nucleotide sequence comprised 1321 nucleotides with only one predicted open reading frame encoding a protein of 435 amino acids, with a predicted Mr 48,840. Structurally, the predicted G protein of aMPV/C maintained similar characteristics to the human respiratory syncytial virus (hRSV) attachment G protein, including two mucin-like regions (heparin-binding domains) flanking both sides of a CX3C chemokine motif present in a conserved hydrophobic pocket. Comparison of the deduced G protein sequence of aMPV/C with that of aMPV types A, B, and D, as well as hRSV revealed overall predicted amino acid sequence identities ranging from 4 to 16.5%, suggesting a distant relationship. However, G protein sequence identities ranged from 72% to 97% when aMPV/C was compared to other members within the aMPV/C subtype or 21% for the recently identified human metapneumovirus (hMPV) G protein. Ratios of non-synonymous to synonymous nucleotide changes were greater than one in the G gene when comparing the more recent Minnesota isolates to the original Colorado isolate. Epidemiologically this suggests some form of positive selection among U.S. isolates since the first outbreak of TRT in the U.S.